leahy



g R; A. LEAHY METHOD OF AND APPARATUS FOR SCREENING GRANULAR MATERIALS 2 Sheets-Sheet l `Original Filed March 2B. 193.1g

Aug 9, w27. Re. 16,761

METHODOF AND APPARATUS FOR SCREENING GRANULAH MATERIALS R. A. LEAHY Origina@ Filed March 28, 1921 2 Sheets-Sheet 2 Reissued Aug. 9, 1927.

UNITED STATES RICHARD A. LEAHY, OF BONNE TERRE, MISSOURI.

METHOD OF AND APPARATUS FOR SCREENING GRANULAR MATERIALS.

Original No. 1,458,067, dated May 22, 1923, Serial reissue filed December 18,

This invention relates to the'art of screening granular materials.

One object of my invention is to provide a method of and an apparatus for Screening granular materials that causes the particles of the material-to be stratified according to their relative masses or sizes, if the material is homogeneous) in such a way that the heaviest or coarscst particles of the material will be forced upwardly to the top of the layer of material and the lightest or finf particles will be brought in direct. contact 'with the screening medium` thereby causing the lightest or finest particles of the material to pass through the meshes or openings in the screening medium without hindrance by the particles which are too large to pass through said openings or meshes.

Another object is to provide an apparatus for screening granular materials that materially increases the eiciency of the screening mediumf and overcomes the necessity ofdiscontinuing the screeninglr operation at frequent intervals and cleaning the screening medium, as is necessary with the methods heretofore in general use.

Other objects and desirable features of my invention will be hereinafter pointed out.

In accordance with this invention a .stretched screening medium is vibrated by deflection thereof intermediate its ends; each upward movement of the medium is, however.v suddenly arrested. so that each vibration is checked. This is accomplished by impartingr afcomparatively slow downward deflection to the medium, releasingT the same in order to cause aV quick upward movement of the medium and suddenly arrestingr the medium in its upward movement. The screening medium is acted upon by a spring, which is compressed during the downward deflection so as to store energy in the spring; upon release of the medium the stored or accumulated energy isa'pplied to accelerate the medium upwardly until suddenly arrested. ,v f

Briefly described. my improvedl apparatus consists of a flexible screening medium that is held under rtension, and means for subjecting said screening mediumj-'to such action that the particles of materialthereon will be thrown upwardly with a force pyro-v portional to their masses (or sizes, if lthe material being screened is homogeneous),

No. 456,431, filed March 28,- 1921. Application for 1923. Serial No. 681,441.

thereby causing the heaviest or coarsest particles of the material to be forced to the top of the layer of material on the screening medium and the lightest or finest particles to come in direct contact. with the screening medium and pass through the openings or meshes in same. The screening medium is preferably inclined or arranged at an angle so as to cause the material to spread out in alayer and flow downwardly over same by gravity. and said screening medium is subjected to a differential vibrating motion at one or morepoints, so as t0 cause a slow downward movement and a quick or sudden upward movement of the screening medium, which latter is suddenly arrested or checked. thereby causingr the heaviest particles of the material to be moved upwardly into a position where they will notobstruct the passage of the finer particles of the material through the screening medium. This treat-ment of the material being screened not only causes the particles to vbe stratified according to their relative masses or sizes and insures the lightest or finest particles passing freely through the screening material without hindrance by the particles which are too large to pass through the meshes of the screening medium, but it also prevents the-openings or meshes of the screening medium from becoming permanently blinded or clogged by particles of material of approximately the same size as the meshes but which are just too large to pass through the meshes. Accordingly, my apparatus increases the efiiciency of .the screening medium and decreases the screening area necessary, by bringing the smallest particles in direct contact with the openings or meshes in the screening medium, and it overcomes the necessity of discontinuing the screening operation at frequent intervals and cleaning the screening mediumA so as to remove the particles that have become clogged in the openings or meshes of the screening medium.

Various fo'rms of apparatus may be used to practice my method, but I prefer tense anv apparatus that comprises a. flexible screening medium stretched taut between two points and arranged in an inclined position. and Ameans for imparting an arrested vibrating motion to one or more zones of said screening medium extending transverseentire width of same so as to comparatively slow and an accelerated, quick, but arrested movement upwards beneath the er oi.I material resting on the. screening ne`v um.

lEig-uref; l and 2 of the drawings are dialmatic views, illustrating the principle which my apparatus operates. iiggure, is a front end elevational View of the apparatus. l

liigure i is a longitudinal sectional vlew ol said apparatus. I n Figure is an enlarged top plan View or a. portion of said apparatus.

Figure 6 is a transvl rse sectional View, teiten o\n the line 6-6 ot' Figure and Figure 7 is a longitud-` sectional View, taken on the line 7 7 of Figure G.

In Figures land 2 X designates a flexible screening;r medium that is held in tension be,- tween 'the lined lines of support A-A and `l7-l?. An arrested Vibrating motion is applied to the screening medium X at one or more points extending' transversely across the entire Width ot said screening medium so that it obtains a comparatively slow movement Cl \f'/i1.:ards, represented by the arrow m in Figure l, and au accelerated` quick but larrested movement upwards, indicated by the arrow n, beneath the layer of material restingv on the screeningl medium Y. The eilect of this arrested motion on the particlcsot material on the screeningr medium Ais to throuthem upwards "withla force proportional tothcir masses (or sizes, it the material homogeneous), the heaviest or coal-sost particles of the material being forced to the top of the layer and the' lightest or tinest particles coming in Contact with the'screening medium and freely through the meshes or openings in same without being: hindered byl those particles of material which are too largo to pass through said meshes, This arrested vibrating motion also )reveals the o ieninffs of the vscrecnin" material from becoming permanently blinded by 'particles that are just too large to pas's thi-(nigh said meshes, as an) particles likely te catch in the uushcs are thrown upwardly by the accelerated motion. represented by the. arrow u. in Figure l.

The screening medium X preferably inclined downwardly Afrom to ll, as shown in Figure L', so as to cause the arrested ribratiug motion lo also impart a forward motion to the particles oi' material remainl iwf on top oiE the screening medium, thus he particles which are too large to :hes to be carried downnd di nharged at the eeuimr medium.

' screened apcdiani in a continu- .:al practice in ore and movementY maar l coal dressing plants, the nnest particles o1' material immediately pass through the openings or meshes in the screening medium on coming in Contact with the upper end portion of the screening medium X, thus leaving the larger part ot the screening; area for the separation of those particles more nearly the same size as the opening or meshes through which they should pass. The stratification is completed on the lower end portion oi the screening: medium which subjected to the arrested vibrating motion, said vibrating motion als@l preventing the openings of the screening` medium from bes coming permanently blinded or clogged with particles of the material.

ln practice I prefer to apply the arrested vibrating motion to only the lower end portion of the screeningr medium X, but in View ot' the fact that the screeningr medium is flexible and under tension, and is connected only 'at' its opposite ends to the supporting structure which carries it, the entire. screening medium will vibrate betweenthe two points A, andB` the minimum vibration being applied 'to the upper end portion of the screeningv medium through which the finest particles of the material pass, and the maximum vibration being applied to the lower end portion ot' the screening medium over which the r'oarsest particles of tle material-travel. This zone of maximum vibration extends uniformly across the entire screening area` transrerscly of the direction ont the material over the screening medium. Accordingly, all the particles passing' through the Zone of minimum vibration which are too large to escape through the.

meshes in thel portion of the vscreening medium corstitilting this 'zone must pass through the Zone of maximum vibration hct'ore reachingglr the point B of .final discharge for the 'over-sized particles.

The apparatus can be constructed in variousl ways` but l prefer to equip it with a l/exibh-'screenng medium X consisting of a strip ot wire cloth or punched sheet metal suspended within a rectangularlyshaped frame composed of side pieces 1 and end pieces 2 arranged inan inclined position on a supporting structure 3, as shown in Figure fl. The lower end oi the Screening medium K is" preferablxr clamped between two lransversely-disposcd bars 4 that are permanently connected in anv preferred manner to the trame within which the screening medium is nranc'ed. und the upper end of the prrlorated strip X that constitutes the screenin;Y medium of the apparatus is clamped be tween two iransverscly-disposed bars 5 that are connected by means of tension bolts 6 to the upper cross piece 2 of the rectangularly-shaped frame in which the screening.,r medium is arranged. The tension bolts (Snot only serve to hold the screeningl medium under sucient longitudinal tension to make said lmedium resilient, but they form an easily adjustable means for varying the tension of the screening medium. The screening medium X is prcfe 'ably provided at its longitudinal side edges with upwardly-projecting flexible flanges 7, as shown in Figure 6, so as to prevent the unriccned materialfrom'escaping from the fide edges ot the screening medium, but said side edges are not connected to the side pieces 1 of the V4frame in which the screening medium is stretched.A

Various means can be used for imparting t-lie differential vibrating motion to the screening medium X of the apparatus, but I prefer to use anieans consisting ot a multiple toothed cam 8 connected to an operating shaft 9 and arranged to cooperate with a tappet 10 that is connected by means of a rod 12 to a wooden cross beam 11 that extends transversely underneath the screening medium X across the entire width of saine. The upper end of said rod is threaded into the tappet 10 and the lower cnd portion of said rod is secured to the cross beam by nuts or in any other suitable way, the cross beam being fastened to the screening nie,- diuiii X by wooden screws or in any way that will cause the screening niediiiiii to vibrate when the cross beam 1l moves upwardly and downwardly. The tappet 10 is held against the face of the calii 8 bysi leaf spring 13 rigidly connected at one end to a transversely-disposed supporting iiieiiibei' 14 arranged above the screening medium. said spring having its opposite eiid adjustably connected to the tappet rod ll by means of nuts l5. which can be adjusted so as tol vary the tension of the spring 13. At each cycle of operations ot' the shaft 9. the cross beam or member l1 willmove downwardly slowly. followed by an accelerated upward niovenient that suddenly arrested by the tappet l() striking against the cam S which virtually acts as an anvil. thereby causing the particles of material on the screening medium' to be thrown upwardly with a toi'ceproportional to the massesot said particles. The operating shaft 9is` joiii'iialed in bearings 16 on the transversely-disposed supporting ineiiibel and is provided with a pulley 17 that is adapted to co-operate with a driving belt (not shown), the supporting member 14 being rigidly connected to the'side pieces g1 of the frame in which the screening medium is stretched. Then the apparatus is equipped with a twelve-toothed cam. the cani shaft S) is preferably operated at about Q00 R. P. M.. so as to impart about 2400 vvibrations per minute to the screening medium. 1f the cam 8 iseqnipped with teeth about .-fq of an inch high, the maximum vibration of the screening medium X will be about 11g of an inch vertically. rl`he power consumption of Such aii apparatus is exceedingly slight, as Ihave 'found that less than l/L H. P. is suic'ientto drive a 3 ft. screen at 2400 vibrations per minute with ay full load.

In the various kinds of screening devices heretofore used for screening granular material the openings or meshes of the screening medium become blind after a short period of operation. This blinding decreases the screening efficiency sometimes more than W. lVheii this occurs it is necessary to stop the screening` operation and clear the openings or meshes of the screening medium by hammering the screening medium or striking it a blow with a stick or other dcvicc. Sometimes vater sprays are used in wet. screening in an endeavor to prevent the. screening medium from becoming blinded or clogged, but it has been found that water sprays will not keep the screening medium clean and the meshes of same unobstructed. My improved apparatus overcomes the ahove-iiientioned characteristics of the screening device heretofore in use, as the arrested vibrating motion which is applied to the screening medium prevents the particles of material from becoming clogged in Ythe meshes of the screening medium. In fact, I have found in dry screening material of a dainp or sticky nature, such. for example, as mine. run ore containing three or four per cent. moisture` the openings or meshes of the screening medium are kept free by the arting the free particles to pass through the openings or meshes of the screening medium.

My invention not only inereasei the et'- liciency ot the screening medium of an apparatus used for screening graniilai material. and reduces the time required to screen such material. due to overcoming the necessity of discontinuing the screening operation at frequent intervals and cleaning .the screening medium ot' the apparatus, but it also increases the speed of the material` passing over the screening medium, thereby making it possible to diminish the slope or :ingle of the screening medium .of the apparatus and thus reduce the head room required in the mill for the apparatus.

In accordance with this invention,l thereforer` the vibration tis not a sustained or free one` but rather a checked and forced one. At the end ot each downward deflection the screening medium is released so as to move quickly upwardly. due to its own tensionv and the tension of the accumulator spring 13. If now the mechanism were then left. to vibrate lfreely untilfdampcd diie to its own resistance, the particles on and especially those in the screen meshes, would tend to vibrate with the medium without becoming fully dislodged. l/Vhere, however, the quick upward movement is suddenly arrested, the vibration is not only merely damped but checked and wholly arrested; accordingly this sudden stoppage will cause the particles to be thrown violently upwardly and not only become dislodged, but to become in fact stratified in accordance'vwith their-masses, so

that the liner particles will remain nearer the medium so that the screening efficiency will be a maximum. screening medium, its release and its checking is at regular intervals, corresponding to the number of teeth on and the speed of rotation olz the cam S; accordingly the vibration is a 'forced one as distinguished from a free or unrestr'ained vibration. This enables the screen to be adapted for various materials by control of the number of vibrations, the screen tension and the strengthrot the spring 13, and the amplitude ot the vibration. The deflection is applied to a stretched screening medium and intermedi ate its ends and the arrest is of the medium itself, as distinguished from a vibration applied to a frame in which the medium is stretched or mounted. The latter arrangement would still leave the medium itselt tree to vibrate atter the frame was arrested, while in accordance with this invention the screen itselt is deflected, released and arrested, thereby not only avoiding the rapid movement ot a heavy trame, but also causing the medium itsel't by its own inherent flexibility to properly act on each particle, It has been Jfound that superior results are produced if the deflection is along a line nearer the lower end of the screen, especially since the vibration is a forced and inter.- rupted one; this moreover provides a longer surface to the zone of maximum vibration.

lt is obvious that various changes may be made in details without departing from the' spirit of this invention; it is, therefore, to bey understood that this invention is not to be limited to the specific details shown and described.

Having thus described my invention, what I claim as new and desire to secure by Let-` ters Patent of the United States is:

l. An apparatus for screening granular material, comprising `a flexible screening medium arranged in an inclined position and held under longitudinal tension, y'the side edges of said medium being free to vibrate, and means connected directly to said screening medium at a' point intermediate its ends and extending transversely across the entire width ot same 'for vibrating said medium upwardly and downwardly so as to impart a comparatively slow downward movement to said screening medium followed by an arccelerated upward movement that is suddenly arrested, thereby causing the particles ot material on said screening medium to be to the masses of said particles.

The deflection of thel thrown upwardly with a force 2. An apparatus for screening granumlar material, comprising a flexible screenlng medium arranged in an .inclined position. and held under longitudinal tension, the sido edges of said screening medium being free to vibrate, a rigid member arranged transversely across said screening medium adjacent the lower end ot same'and connected directly to said screening medium, and

proportional i nected to said member angl a cooperating*` anvil against which said part `strikes so as to suddenly arrest the upward movement of said screening medium, thereby causing the particles medium to be thrown upwardlywit-h a force proportional to the massesof said. particles.

3. An apparatus for screening granular material, comprising a stationary frame'arranged in an inclined position, 'a piece of mesh material held in said frame undersufcient longitudinal tension to produce. a flexible' screening medium having inherent resiliency, the side edges of said screening medium being free tovibrate, an operating shatt arranged transversely of said frame,

.a transversely-disposed, rigid member connected directly to said screening medium and extending across the entire width of same, and means actuated by said operating shaft for imparting a differential vibrating motion to said transversely-disposed, rigid member comprising a part connectedto said member, and a co-operating anvil against which said part strikes so as to suddenly arrest the upward movement o said screening medium, thereby causing the particles ot' material on said screening medium to be thrown-upwardly with a force proportional to the masses of said particles.

4. An apparatus for screening granular' material, comprising a frame arranged in an inclined position, a strip of leXible screenmg medium arranged between the side pieces ot said trame in such a way that the side edges of said medium are free to vibrate relatively to said side pieces, means for4 connecting the endsot said screening' medium to the top and bottom cross pieces of the trame and holding said medium under sufficient longitudinal tension to make said Amedium resilient, a transversely-disposed,

rigid member connected directly to said screening medium and extending across the entire width of same, an operating shaft supliorted at a point above said screening medium, and a tappet mechanism operated by said shaft for vibrating said member upwardly and downwardly, comprising a cam on the shaft and a cooperating part on said member that strikesagainst said cam with of material on said screening Btl thereof intermediate its ends, releasing' the ,/same, suddenly arresting-each upward moveterials comprising,

ment of the medium and before 1t reaches the yend of its otherwise normal upward vibrating movement, and passing the material over the vibrating medium, whereby the particles will be thrown upwardly with forces proportional to their masses.

^ 6. The method of screeninggranular mavibrating a screening medium, stretched in an inclined position, by deliection downward thereof intermediate its ends while the material is fed thereon, releasing the same, and suddenly arresting each upward movement of the medium and before it reaches the end of its otherwise normal upward vibrating movement, vwhereby the particles will be thrown upwardly and passed along the medium.

7. The method of screening granular materials comprising, vibrating a stretched screening medium by downward deflection thereof at definite time intervals intermediate its ends, releasing the same, suddenly arresting the upward movement of the medium at the end of each interval and bctore it reaches the end of its otherwise normal upward vibrating movement, and passing the material over the vibrating medium.

8. The method of screening granular materials, comprising, imparting at regular intervals a downward'movement to a stretched .Jcreeniug medium interlnediate its ends, releasing the medium at the end of each downward movement so as to Vcause it to move uwvard'ly, suddenly arresting the upward movement otl the medium and before it real-hes the end ol its otherwise normal upward vibrating movement, and passing the material over the vibrating medium.

E). The method of screening granular 1naterials con'lprising, imparting at regular iutervals a comparatively slow downward movement to a stretched screening medium intermediate its ends, releasing the medium at the end ot each downward movement so as to cause i l to move quickly upwardly, suddenly arrest'ng the upward movement ot the medium and before it reaches the end of its otherwise normal upward vibrating movement, and passing the material over the vibrating medium.

l0. The method of screening `granular materials comprising. defleeting 'a stretched screening medium downward v intermediate its ends while energy is store in an. accumulator, releasing the medium and applying the stored energy thereto. suddenly arresting the-upward movement of the medium and before it reaches the end of its otherwise normal upward vibrating movement, and passing the material over the medium. l

11. The method of screening granular mateiials comprising, imparting at regular intervals, to a screening medium stretched inv al1-inclined position a downward movement ncarerits lower end, releasing the medium at the end` of each downward movement` suddenly arresting each upward movement of the medium and before it reaches the end of its otherwise normal upward vibrating movement, and passing the material over the medium and through the zone of maximum vibration.

12. An apparatus for screening granular materials comprising, a pair ot end supports, a screening medium stretched between said supports, means for vibrating said medimn by downward deflection and release thereof, and means for suddenly arresting each npward movement of the medium and before it reaches the end of its otherwise normal upward vibrating movement adapted to stop the vibration and throw the material particles upwardly.

ward deflection and release thereof, and

means for suddenly arresting each upward movement of the medium and\ before it reaches the end of its otherwise normal upward vibrating movement,adapted lo stop the vibration and throw the material particles upwardly and along the medium.

14. An apparatus for screening granular n'laterials comprising. a pair of end supports, a icreening medium stretched between said supports. means tor vibrating said medium by downward deflection and release thereof at regular time intervals. and means for suddenlyY arresting the upward movement ol' saidl medium at they end of each interval and before it reaches the end of its otherwise normal upward vibrating movement.

l5. An apl'iaratus for screening granular materials comprising, la pair of end supports, a screening` medium stretched between said sui'iprnts. means vfor deflectingsaid me-A dium downwardly at regular intervals and for releasing the same at the end of each deflect ion. and means for suddenly arresting the upward movement of said medium at the end ot each interval and before it reavhrs the end of its otherwise normal upward vibrating movement.

said supports, m-eans t'or imparting a comdownwardly intermediate iis ends and for tensioning' said spring; and means fm" rar leasing said medium adapted t0 suddenly arrest the upward movementthereof and be for@ ranches the end m" ita @ihm mai upward. Vlbx'atmg nmvanumi..

1S. An apparatus for scz'wenia'ag; grandi-1? matcrlah comprismg, a par? of' Lad sup 2' ports, a Screening mediumstrnaad in a- 'inclined positin between "aid Suppm'h' means acting on Said mcd? m mayer lower and adapted tu defiant 'the .Cama o ardlyg and Ixeans 10:' wlmming sai@ umd! :mism adapted toxuf'dmxy arres the u, ward movement thm'eo and nefmja if; ref upward VE braking n'loven'lent.

Signed at Si. im' day of Decenfaber.. 3S 

